Carbohydrates represent the largest fraction of biomass, and various strategies for their efficient use as a feedstock for the preparation of commercial chemicals are being established. Biomass is of particular interest due to its potential as supplementing, and ultimately replacing petroleum as a feedstock for such purposes. Carbohydrates obtainable from biomass comprise C6 and C5 sugars and are of particular industrial interest as they are a potential source of highly functionalised short chain carbon compounds. This is of particular importance for highly functionalised short chain carbon compounds that are commercially unavailable, such as 2,5,6-trihydroxy-3-hexenoic acid and 2,5-dihydroxy-3-pentenoic acid and esters thereof. A general way to denominate these compounds is alpha-hydroxy-beta-ene-acids and esters thereof. The general molecular structure of such compounds isR′—HC═CH—CHOH—COOR  (I)Where R′ and R represent —H, -alkyl or hydroxyalkyl groups.
Currently, 2,5,6-trihydroxy-3-hexenoic acid and 2,5-dihydroxy-3-pentenoic acid are prepared by alkaline degradation of cellulose: Svensk Papperstidning (1974) 16, p 593-602 and J. Appl. Polymer Sci. (1978) 22, pp 615-623; and mannan: Acta Chem Scan. (1980) 40, pp 9-14. However, the product compositions of these reactions comprise numerous compounds, and therefore the products obtained are in low yields (5 mg per g of product). Additionally, the methods proposed are not industrially feasible due to the variety of reaction products produced in the process.
It is known that sugar compositions comprising C6 and/or C5 sugars may be substrates in the preparation of methyl lactate in the presence of Sn-BEA. EP 2 184 270 B1 and Science (2010) 328, pp 602-605 report yields of methyl lactate of 64%, 43% and 44% at 160° C. in methanol from sucrose, glucose and fructose, respectively. Numerous by-products are, however, observed in connection with this reaction, and the major by-product reported is methyl vinylglycolate (3-11%).
It has been suggested that small amounts of compounds similar to saccharinic acids, including a noticeable amount of highly polar products may be produced during the disclosed reaction. It has been postulated that these highly polar products are methyl esters of C6 saccharinic acids. Such C6 saccharinic acids are described in Carbohydrate Res. (1996) 280, pp 47-57. However, this reference is silent with regard to the identity, the amount in percentage yield and the number of compounds that are components of the highly polar products.
Green Chem. (2012) 14, pp 702-706 discloses similar reaction conditions to Science (2010) 328, pp 602-605, wherein the temperature of the reaction is varied. The combined yields of identified products and unconverted sugars are at least 51%.
ChemSusChem (2015) 8, pp 613-617 discloses an increase in methyl lactate yield (from 20-25% to 66-71%) obtained from sugars in the presence of a heterogeneous stannosilicate catalyst when an alkali ion is added to the reaction process.
Accordingly, it is desirable to provide a Lewis acid based catalytic processes for the preparation of highly functionalized C6 and C5 compounds. Additionally, it is desirable to provide highly functionalized C6 and C5 compounds in high yields by way of industrially applicable, direct, selective processes.